/dev/xxx: open failed: No medium found
Insufficient free extents (0) in volume group VolGroup00: 1 required
Rounding up size to full physical extent xx.00 MB
Snapshot create failed
Error occured because you do not have sufficient free extents in volume group to create snapshots. Free extents are used by LVM to create snapshots. The amount of free extents that are required will depend on the amount of data on the volume that changes over the duration of the backup. When configuring the backup set and setting the snapshot size, be sure to set the number large enough so there are no problems with the backup.
Check that you have sufficient free extents available on the volume group to create snapshots.
Use lvdisplay to check the volume. If you have insufficient free extents then you must add physical volumes to the group.
For more information on the procedure to resize an LVM2 logical volume please refer the following Redhat Knowledgebase article here.